talk with her classroom teacher first

Ask teacher's general opinion ( strengths and weaknesses) about your daughter.

If teacher's opinion matches pretty well with yours about your daughter, you can tell teacher that lately your daughter told you that she had been bullied by XXX (giving detail about events) in school. You daughter are very unhappy. You want to work with teacher to help your daughter.

If teacher's opinion is far worse from yours, you should ask for more detailed information to figure out why teacher thinks that way. Then go home and think about that. You need to figure out if your daughter needs to change or teacher’s opinion is wrong. You need to set more meetings with teacher until teacher’s opinion matches yours.

The point: making sure that the classroom teacher has right impression about your daughter. So teacher can be your daughter's side when bullying happens.